1. Field of the Invention
The present invention relates generally to the field of intravascular catheters. More particularly, the present invention relates to an apparatus, system, and method for the flow-directed introduction of catheters to a patient's vasculature.
Flow-directed catheters are designed so that the flow of blood through an artery directs the catheter tip along the arterial flow path and to the target site. One type of flow-directed catheter uses an enlarged balloon or cup-shaped end to create a partial obstruction causing the blood flow to pull the tip of the catheter in the direction of the blood flow. See, for example, U.S. Pat. Nos. 3,995,623 to Blake et al. and 4,024,873 to Antoshkiw et al.
Another type of flow-directed catheter has a very flexible distal end which is designed to be carried along by the blood flow instead of by partially blocking the artery. One of this type is manufactured by Balt S.A. of France under the trademark MAGIC. It is made of a hydrophobic material with a relatively stiff proximal section, a moderately flexible midsection and a quite flexible distal section. While this catheter has enjoyed some success, it has several shortcomings. The inside diameter of the distal section is quite small and is often not usable with a guidewire. If a guidewire is used the guidewire tends to pull on and stretch the distal section and damage the floppy tip. A guidewire could also puncture the wall of the distal section. The MAGIC catheter also includes a region of intermediate stiffness between the relatively stiff proximal section and the very flexible distal end. While facilitating a catheter introduction, such a transition section requires an additional bond within the catheter body to accommodate the additional section. The additional bond, in turn can create a constriction on the inside of the catheter lumen which can obstruct the relatively weak distal section of the catheter and can block the catheter during infusion of various agents. Blockage can cause rupture of the catheter, placing the patient at risk.
Another prior art flow-directed catheter is manufactured by Target Therapeutics of Fremont, Calif. and is sold under the trademark Zephyr. It is intended to be used with a mandrel which allows the stiffness of the entire catheter to be increased during introduction through a guide catheter. The mandrel is removed before the catheter is advanced into the vasculature. The Zephyr has a lubricous, hydrophilic coating on its outside surface to aid passage of the catheter through the guiding catheters and vessels. A problem with this catheter is that it suffers from the similar limitations of the Magic catheter due to its small diameter. Also, this catheter is too stiff to access distant vascular structures. See U.S. Pat. No. 5,336,205.
Heretofore, flow-directed catheter designs have had to compromise between flexibility, which is required for the distal portion to follow blood flow, and column strength, which is required to advance the catheter from its proximal end. In order to properly balance such contrary objectives, catheters having multiple zones of flexibility have been proposed. For example, U.S. Pat. No. 5,336,205, describes a catheter having a proximal zone which is relatively rigid, an intermediate zone having an intermediate flexibility, and a distal zone which is highly flexible and capable of following blood flow. While a workable compromise, the length of the distal zone is sometimes too short for a desired treatment protocol. While catheters having flexible regions of different lengths could be provided, the need to maintain an inventory of multiple catheters is undesirable. Additionally, even if an inventory of catheters having transition zones of different lengths were available, it is often not possible to predict which length would be most effective for treating any individual patient or condition. Thus, after starting a procedure, it would often be necessary for a physician to exchange catheters having transition zones of different lengths if the initially chosen catheter is unable to access the treatment site. The need to exchange catheters increases the cost, duration, and risk of patient complication.
A second problem faced by many flow-directed catheters is the need to occasionally rely on a guidewire to guide the catheter past branches in the vasculature. Because of the small dimensions of prior flow-directed catheters and the high surface friction of the materials normally used in the flexible distal sections of such catheters, it has been very difficult to employ conventional guidewires to assist in catheter placement. Moreover, the additional constrictions resulting from the bond(s) required to accommodate the intermediate transition section(s) create another potential impediment to guidewire advancement. Thus, for use with flow-directory catheters, guidewires should have a highly lubricous surface, be very radiopaque (to permit visualization), should have shapeable distal sections, and should also have soft, atraumatic tips. No one guidewire currently available meets all of these requirements adequately.
For these reasons, it would be desirable to provide flow-directed catheters, flow-directed catheter systems, and methods for introducing flow-directed catheters which overcome at least some of the shortcomings discussed above. In particular, it would be desirable to provide flow-directed catheters where the stiffness of the most flexible regions of the catheter could be varied while advancing the catheter through the vasculature. It would be further desirable to provide catheter systems and methods for introducing such catheters which facilitate use of guidewires for occasionally advancing the flow-directed catheters through portions of the vasculature. Such catheter and guidewire systems should allow the catheter to be introduced by flow, by pushing (with the catheter selectively stiffened with an internal guidewire), or by guiding over the guidewire.
2. Description of the Background Art
U.S. Pat. Nos. 5,336,205; 4,024,873; and 3,995,623, have been discussed above. Another flow-directed catheter design is shown in copending application Ser. No. 08/399,677, assigned to the assignee of the present invention. Microcatheter designs having regions of varying flexibility are described in U.S. Pat. No. 4,739,768 and copending application Ser. No. 08/534,089, assigned to the assignee of the present application. Catheters having radiopaque fillers in their bodies are described in U.S. Pat. Nos. 5,171,232 and 4,469,483. A flow-directed catheter having a lubricous coating is described in WO 96/01662. Catheters having surface irregularities to reduce sliding friction with coaxial catheters are described in U.S. Pat. No. 5,496,292; WO 93/23105; and WO 92/19308.